SC17 - alkali Metals

Question 1

What are the properties of lithium ?

Answer 1

Lithium has the electron structure (2,1).

Lithium is the least reactive of the alkali metals.

Lithium burns with a crimson flame when it reacts with oxygen.

Lithium floats on the surface of water and will release bubbles of hydrogen gas (it effervesces)

Question 2

What are the properties of sodium ?
Seneca

Answer 2

Sodium has the electron structure (2,8,1).

Sodium is more reactive than lithium because its outer electron is less strongly attracted to the positively charged nucleus. This is because it is a greater distance from the positive charge of the atom’s nucleus.

The metal floats on the surface of water, which releases enough heat to melt the sodium. The sodium moves quickly across the surface of the water.

Sodium burns with a yellow/orange flame when it reacts with oxygen.

Question 3

What are the properties of potassium ?
Seneca

Answer 3

Potassium has the electron structure (2,8,8,1).Potassium is more reactive than lithium and sodium because its outer electron is least strongly attracted to the nucleus.The metal floats on the surface of water, and has a similar, but more vigorous, reaction compared with sodium.Potassium burns with a lilac flame when it reacts with oxygen.

Question 4

Trend in group 1 and 2
Seneca

Answer 4

All group 1 (and group 2) elements end withium.

Question 5

Alkali metals reactions with chlorine
Seneca

Answer 5

A metal chloride is formed (e.g. sodium chloride), which dissolves in water to give a colourless solution.

Question 6

Alkali metals reaction with oxygen

Answer 6

Rapidly turns from silvery shiny to dull as a metal oxide (e.g. potassium oxide) is produced.

Question 7

Alkali metals reaction with water
Seneca

Answer 7

The metal floats on the surface and melts to create a metal hydroxide (e.g. lithium hydroxide).When they react with water, the energy released is enough to melt the metal.

Question 8

Reactions of reactive metals with water

Answer 8

Potassium, sodium and lithium all react quickly with cold water to produce a metal hydroxide and hydrogen gas.

Question 9

Potassium reaction with water

Answer 9

Potassium is the most reactive so reacts very quickly.The hydrogen produced ignites instantly and the metal also sets alight, sparking and burning with a lilac flame.

Question 10

Sodium reaction with water

Answer 10

Sodium fizzes rapidly and melts to form a ball that moves around on the water surface.

Question 11

Lithium reaction with water

Answer 11

Lithium fizzes steadily and floats, becoming smaller until reaction complete, unvisible.

Question 12

Electron shells affect on reactivity

Answer 12

there are more electron shells in between the nucleus and outer electron, which shields the electron from the nuclear charge.This means that the electron is more easily lost, so the atom is more reactive.

Question 13

Halogen properties

Answer 13

Elements in group 7 in the periodic table are called halogens. They have 7 electrons in their outer shell. They are very reactive because they easily accept an electron into this outer shell. They have similar properties and react in similar ways.

Question 14

Salts of a halogen properties

Answer 14

When a metal atom transfers its outer electron to a non-metal atom (like a group 7 atom), salts are formed.The result is a compound where all the ions have a full outer shell.

Question 15

Reactivity trends in halogens

Answer 15

Reactivity

As you go down the group, the halogens become less reactive. This is because:The atoms gain more electron shells.The outer electron shell is further from the nucleus.The attraction between the nucleus and the electron (to be gained from another element) decreases.

Question 16

How are halogens presented (something to remember)

Answer 16

In their elemental form, halogens share electrons to make diatomic molecules (molecules made of pairs of atoms).

Question 17

States and colours of halogens

Answer 17

Colours and States of Halogens

At room temperature, the following three halogens have these properties:

Chlorine

Colour: pale green.State: gas.

Iodine

Colour: dark grey.State: solid.

Bromine

Colour: red-brown.State: liquid.

Question 18

Test for Chlorine

Answer 18

Insert damp litmus paper into a test tube containing a gas.If the gas is chlorine, the litmus paper will bleach and change colour from red to white.

Question 19

Reaction between metals and halogens

Answer 19

When a metal atom transfers its outerelectronto a halogen, asaltis formed.

e.g. 2Na + Cl2→ 2NaCl

Question 20

Noble gas (Group 0) uses

Answer 20

Noble gases can be used in light bulbs because they will NOT react with the hot metal filament.

Question 21

Noble gas reactivity

Answer 21

Because noble gases are unreactive, they exist as single atoms (monatomic) instead of forming molecules.

Question 22

Noble gas boiling points

Answer 22

The noble gases have low boiling points.But their boiling points do increase as you move down the periodic table. This is because the relative atomic mass increases lower down the periodic table.

Question 23

Noble gas density and uses

Answer 23

The noble gases (in group 0) have low densities.Their densities do increase as you move down the periodic table because of their increasing relative atomic mass.This low density makes them useful in balloons.

Question 24

Reaction between a halogen and a metal

Answer 24

metal + halogen → metal halide
Chlorine example

(EXAMPLE) Sodium + chlorine → sodium chloride2Na(s)+ Cl2(g)→ 2NaCl(s)

Question 25

Metal halides properties

Answer 25

Ionic compounds that are solid at room temp

Question 26

What are hydrogen halides ?

Answer 26

Halogens react with hydrogen to form hydrogen halides. Hydrogen halides are covalent compounds.

Question 27

What type of solutions do hydrogen halides form when reacting with water ?

Answer 27

Acidic solutions

The hydrogen halides dissolve in water to form acidic solutions, such as hydrofluoric acid, hydrobromic acids and hydroiodic acid.Hydrogen chloride dissolves in water to form hydrochloric acid.The solutions produce H+ions, which make them acidic.

Chlorine example

Hydrogen + chlorine → hydrogen chlorideH2(g)+ Cl2(g)→ 2HCl(g)

Question 28

What does hydrogen chloride form when it dissolves in water?

Answer 28

Hydrochloric acid

Question 29

Define a spectator ion ?

Answer 29

Aspectatorion is an ion that doesn’t change during a chemical reaction.

Question 30

.

Answer 30

.

Question 31

Displacement as redox reactions

Answer 31

Halogens

More reactive halogen

Each atom gains an electron

Reduced

Less reactive halogen

Each ion loses an electron

Oxidised

Question 32

Explain why reactivity decreases down group 7

Answer 32

The difference in the atoms

-Going down the group, atoms getbigger.
-Theouterelectrons are, therefore, further from thenucleus.
-This means the attraction between thenegativelycharged electrons and thepositivelycharged nucleus arelessstrong.

2

The difference in reactivity

-Group 7 elements react to become ions with a1-charge. This means they gain1electron.
-Down the group, there islessattraction for the outer electrons. This means that the elements gain electronslesseasily.

Question 33

Question 1

A scientist conducts 2 experiments.

Experiment ACl2(g)is bubbled through a solution of NaBr. An orange colour develops as bromine is produced.Experiment BBr2(g)is bubbled through a solution of NaCl. No observations are made.

Answer 33

Explain the observations or lack of observations. Write equations for any reactions that occur.

1

Describe experiment A

Chlorinedisplaces thebromideions in NaBr. This leads to the formation ofbrominewhich is orange.
Cl2+2NaBr →Br2+ 2NaCl

2

Describe experiment B

There are no observations is experiment B becausebrominecannot displace thechlorideions in NaCl.

3

Explain the results

This is becausereactivitydecreasesdowngroup7. Bromine is lower down thanchlorineand is, therefore, less reactive and cannot displace.

Question 34

Why is sodium more reactive than lithium ?

Answer 34

Elements are more reactive if they can give awayelectronseasier to achieve anoblegasconfiguration.

2

Sodium’s outer electron is less strongly attracted to thepositivelycharged nucleus.

3

This is because the outer electron is agreaterdistance from the positive charge of the atom’s nucleus.

Question 35

Why are group 1 elements very reactive ?

Answer 35

Electrons fill an atom’s shells in order of increasing energy.

The closer a shell is to the nucleus, the lower its energy level, so the first shell that is filled is the closest to the nucleus.

Question 36

Why does more shells mean more reactive ?

Answer 36

More shells shields the electron from the nuclear charge of the nucleus, meaning a weaker attraction.